People talk about screen reader compatibility of pull down menus, but an
even bigger problem is for people with low vision who are restyling the
colors and text size of a web page. Most of these pull down menu lists
render very poorly when browsers are set to ignore colors and change font
size.
When author colors are ignored the menu text background is what ever is
over on the webpage, making text un readible.
When font sizes are changed menu text is often clipped.
There maybe certain CSS menu techniques based on list markup that maybe
accessible, but I have not seen any javascript based system that work when
author colors and font sizes are ignored.
Jon